Abstract The inclusive jet cross-section is measured in proton-proton collisions at a centre-of-mass energy of 7 TeV using a data set corresponding to an integrated luminosity of 4.5 fb-1 collected ...with the ATLAS detector at the Large Hadron Collider in 2011. Jets are identified using the anti-k t algorithm with radius parameter values of 0.4 and 0.6. The double-differential cross-sections are presented as a function of the jet transverse momentum and the jet rapidity, covering jet transverse momenta from 100 GeV to 2 TeV. Next-to-leading-order QCD calculations corrected for non-perturbative effects and electroweak effects, as well as Monte Carlo simulations with next-to-leading-order matrix elements interfaced to parton showering, are compared to the measured cross-sections. A quantitative comparison of the measured cross-sections to the QCD calculations using several sets of parton distribution functions is performed. Figure not available: see fulltext.
Abstract The ... production cross-section dependence on jet multiplicity and jet transverse momentum is reported for proton-proton collisions at a centre-of-mass energy of 7 TeV in the single-lepton ...channel. The data were collected with the ATLAS detector at the CERN Large Hadron Collider and comprise the full 2011 data sample corresponding to an integrated luminosity of 4.6 fb -1. Differential cross-sections are presented as a function of the jet multiplicity for up to eight jets using jet transverse momentum thresholds of 25, 40, 60, and 80 GeV, and as a function of jet transverse momentum up to the fifth jet. The results are shown after background subtraction and corrections for all known detector effects, within a kinematic range closely matched to the experimental acceptance. Several QCD-based Monte Carlo models are compared with the results. Sensitivity to the parton shower modelling is found at the higher jet multiplicities, at high transverse momentum of the leading jet and in the transverse momentum spectrum of the fifth leading jet. The MC@NLO+HERWIG MC is found to predict too few events at higher jet multiplicities. Figure not available: see fulltext.
Abstract Searches for heavy long-lived charged particles are performed using a data sample of 19.1 fb-1 from proton-proton collisions at a centre-of-mass energy of ... TeV collected by the ATLAS ...detector at the Large Hadron Collider. No excess is observed above the estimated background and limits are placed on the mass of long-lived particles in various supersymmetric models. Long-lived tau sleptons in models with gauge-mediated symmetry breaking are excluded up to masses between 440 and 385 GeV for tan beta between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered. In the context of simplified LeptoSUSY models, where sleptons are stable and have a mass of 300 GeV, squark and gluino masses are excluded up to a mass of 1500 and 1360 GeV, respectively. Directly produced charginos, in simplified models where they are nearly degenerate to the lightest neutralino, are excluded up to a mass of 620 GeV. R-hadrons, composites containing a gluino, bottom squark or top squark, are excluded up to a mass of 1270, 845 and 900 GeV, respectively, using the full detector; and up to a mass of 1260, 835 and 870 GeV using an approach disregarding information from the muon spectrometer. Figure not available: see fulltext.
Abstract The production of a W boson decaying to enu or muν in association with a W or Z boson decaying to two jets is studied using 4.6 fb-1 of proton-proton collision data at ... TeV recorded with ...the ATLAS detector at the LHC. The combined WW + WZ cross section is measured with a significance of 3.4sigma and is found to be 68±7 (stat.)±19 (syst.) pb, in agreement with the Standard Model expectation of 61.1±2.2 pb. The distribution of the transverse momentum of the dijet system is used to set limits on anomalous contributions to the triple gauge coupling vertices and on parameters of an effective-field-theory model. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) A search for the ... decay of the Standard Model Higgs boson is performed with the ATLAS experiment using the full dataset ...recorded at the LHC in Run 1. The integrated luminosities used are 4.7 and 20.3 fb^sup -1^ from pp collisions at ... and 8 TeV, respectively. The processes considered are associated (W/Z)H production, where W arrow right enu/muν, Z arrow right ee/mumu and Z arrow right νν. The observed (expected) deviation from the background-only hypothesis corresponds to a significance of 1.4 (2.6) standard deviations and the ratio of the measured signal yield to the Standard Model expectation is found to be mu = 0.52 ± 0.32 (stat.) ± 0.24 (syst.) for a Higgs boson mass of 125.36 GeV. The analysis procedure is validated by a measurement of the yield of (W/Z)Z production with ... in the same final states as for the Higgs boson search, from which the ratio of the observed signal yield to the Standard Model expectation is found to be 0.74 ± 0.09 (stat.) ± 0.14 (syst.). Figure not available: see fulltext.
Abstract Several models of physics beyond the Standard Model predict neutral particles that decay into final states consisting of collimated jets of light leptons and hadrons (so-called "lepton ...jets"). These particles can also be long-lived with decay length comparable to, or even larger than, the LHC detectors' linear dimensions. This paper presents the results of a search for lepton jets in proton-proton collisions at the centre-of-mass energy of ... TeV in a sample of 20.3 fb -1 collected during 2012 with the ATLAS detector at the LHC. Limits on models predicting Higgs boson decays to neutral long-lived lepton jets are derived as a function of the particle's proper decay length. Figure not available: see fulltext.
Abstract The results of a search for top squark (stop) pair production in final states with one isolated lepton, jets, and missing transverse momentum are reported. The analysis is performed with ...proton-proton collision data at ... = 8 TeV collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20 fb -1. The lightest supersymmetric particle (LSP) is taken to be the lightest neutralino which only interacts weakly and is assumed to be stable. The stop decay modes considered are those to a top quark and the LSP as well as to a bottom quark and the lightest chargino, where the chargino decays to the LSP by emitting a W boson. A wide range of scenarios with different mass splittings between the stop, the lightest neutralino and the lightest chargino are considered, including cases where the W bosons or the top quarks are off-shell. Decay modes involving the heavier charginos and neutralinos are addressed using a set of phenomenological models of supersymmetry. No significant excess over the Standard Model prediction is observed. A stop with a mass between 210 and 640 GeV decaying directly to a top quark and a massless LSP is excluded at 95% confidence level, and in models where the mass of the lightest chargino is twice that of the LSP, stops are excluded at 95% confidence level up to a mass of 500 GeV for an LSP mass in the range of 100 to 150 GeV. Stringent exclusion limits are also derived for all other stop decay modes considered, and model-independent upper limits are set on the visible cross-section for processes beyond the Standard Model. Figure not available: see fulltext.
Abstract A search for the neutral Higgs bosons predicted by the Minimal Supersymmetric Standard Model (MSSM) is reported. The analysis is performed on data from proton-proton collisions at a ...centre-of-mass energy of 8 TeV collected with the ATLAS detector at the Large Hadron Collider. The samples used for this search were collected in 2012 and correspond to integrated luminosities in the range 19.5-20.3 fb -1. The MSSM Higgs bosons are searched for in the tau tau final state. No significant excess over the expected background is observed, and exclusion limits are derived for the production cross section times branching fraction of a scalar particle as a function of its mass. The results are also interpreted in the MSSM parameter space for various benchmark scenarios. Figure not available: see fulltext.
Abstract This paper presents a search for new particles in events with one lepton (electron or muon) and missing transverse momentum using 20.3 fb-1 of proton-proton collision data at ... = 8 TeV ...recorded by the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. A W ' with Sequential Standard Model couplings is excluded at the 95% confidence level for masses up to 3.24 TeV. Excited chiral bosons (W *) with equivalent coupling strengths are excluded for masses up to 3.21 TeV. In the framework of an effective field theory limits are also set on the dark matter-nucleon scattering cross-section as well as the mass scale M * of the unknown mediating interaction for dark matter pair production in association with a leptonically decaying W. Figure not available: see fulltext.
Abstract This paper describes a measurement of the Z/γ * boson transverse momentum spectrum using ATLAS proton-proton collision data at a centre-of-mass energy of ... TeV at the LHC. The measurement ...is performed in the Z/γ * arrow right e + e - and Z/γ * arrow right mu + mu - channels, using data corresponding to an integrated luminosity of 4.7 fb-1. Normalized differential cross sections as a function of the Z/γ * boson transverse momentum are measured for transverse momenta up to 800 GeV. The measurement is performed inclusively for Z/γ * rapidities up to 2.4, as well as in three rapidity bins. The channel results are combined, compared to perturbative and resummed QCD calculations and used to constrain the parton shower parameters of Monte Carlo generators. Figure not available: see fulltext.
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